It's very flexible: the FM capabilities are reasonably well developed, and the mod matrix allows a wide range of control. The range of modes available for the two filters cover pretty much everything you could want, from subtly named emulations like tb, ob and rp to more far out original sounds.

It sounds great. I've never owned a vintage analog synth, so I can't really comment on whether the emulations of classic filters are accurate, but they certainly sound cool. Apparently Alesis placed sound quality first and extraneous bells whistles and gongs second, and in terms of pure, creamy audio indulgence, it shows.

The user interface is intuitive, and fairly easy to learn if (like me) you tend to ignore instruction manuals. Parameters tend to live where you expect them to, rather than in strange and inexplicable submenus. This is greatly helped by the LCD screen.

The mod and pitchbend wheels light up as you move them. And the LFO and arpeggiator LED's flash. It's hypnotic, and beautiful.

At the time of writing, it's at the cheap end of the price range for similarly specced synths, particularly given that it's a keyboard rather than rack model.

Cons

Although four voices of multitimbrality is nice, the eight voice polyphony is pretty weak compared with the competition, particularly once you start stacking the voices in unison mode.

The effects section is very limited - this is one of the bells, whistles and gongs that was cut out. You have one compression / overdrive / distortion effect, and one 'other' effect, chosen from phasing, flanging, chorus, 'slapback' delay or the vocoder. While the effects that are there are good quality, the absence of reverb or proper delay hurts.

Although it's competitively priced off the shelf, unlike a lot of similar synths it is (at the time of writing) a fairly new synth and unlikely to be available cheaply second hand.

It looks a bit like a cheap Star Trek prop. Although this might be a good thing in some people's eyes....

Overall, if you're after a budget virtual analog I'd happily reccommend the Ion. But then I would - I've just bought one.